Fig. 44.—Leather-back or Corded Tortoise (Spargis coriacea).
The Leather-back or Corded Tortoise, Spargis coriacea, differs from every other genus, its body being enveloped in a coriaceous hide; tuberculous in the young, perfectly smooth in adults. The feet are without claws. Seven longitudinal grooves extend from the neck to the tail, which remind one of the seven chords of the ancient lyre. Only one species of Sphargis is known (S. coriacea, [Fig. 44]). This species is found in the Mediterranean and Atlantic Ocean, and is, with the Hawk's-bill Tortoise, the only species found on the British coast. Its body is a light brown, with the lines of the carapace fawn-colour; its members black, edged with yellow. It attains the length of six to eight feet, and a breadth of about one-fifth of the length: it sometimes attains the weight of fourteen to sixteen hundred pounds. Its flesh is said to be unwholesome, and, on being eaten, to produce severe vomiting and purging.
[BIRDS.]
INTRODUCTORY CHAPTER.
Birds are the spoilt children of nature—the favourites of creation. Their brilliant plumage often assumes the most resplendent colours. They have the happy privilege of moving in space—now fluttering through the air, hunting the insect which flits from flower to flower; now soaring high aloft, and swooping upon the victim it has marked for its prey; now cleaving the atmosphere on rapid wing, and performing journeys of vast extent with great rapidity. Mankind have a profound sympathy with these little winged beings, which charm at once by the elegance of their form, the melody of their song, and the graceful impetuosity of their movements.
Anatomically speaking, birds are connected with the Mammifera by their internal structure. Their skeleton essentially resembles that of the Mammals, the bones being nearly the same, only modified slightly for the purposes of flight.
In birds there is a double circulation. The heart consists of two moieties, or lobes, known as the auricle and ventricle. It is conical in form, and occupies the anterior part of the thorax, its apex passing between the lobes of the liver; but there is little perceptible distinction between auricles and ventricles. Their blood is richer in globules than that of the Mammalia, being more thoroughly permeated by air; the respiratory function is also more energetic, from the same cause—in fact, they consume a larger quantity of oxygen, and produce a proportionately greater degree of heat; for while their lungs are small, and placed in the upper part of the thorax only, where they are confined on each side to a cavity, bounded above by the ribs, and below by an imperfect diaphragm, they are perforated by tubes, which communicate with membranous cells, distributed over the thoracic and abdominal cavities, between the muscles, and beneath the skin,—often in all parts of the body. What distinguishes the bird, in fact, is not the wing; for certain of the Mammalia, as the Bat, and even some fishes, as the Gusard and Exocœtus, can traverse the air by expanding their wings. In birds the diaphragm which arrests the air in the Mammalia is scarcely perceptible, so the external air penetrates into every part of the body by the respiratory tubes, which ramify the whole cellular tissue, the interior of the bones, and even the feathers, and between the muscles. Their bodies, dilated by the air inhaled, lose a proportionate amount of weight; balloon-like, they float in the air, and, from their peculiar forms, they can swim, so to speak, in any direction in the gaseous element.
